KAMPALA (Reuters) - Ugandan soldiers sexually abused at least 13 girls and women in the Central African Republic while the troops were helping to hunt for warlord Joseph Kony, the U.S.-based Human Rights Watch said on Monday.

The Ugandan military first arrived in Central African Republic in 2009 and a force of about 2,500 have been stationed there. They are part of a U.S.-supported African Union force seeking to defeat Kony and his Lord’s Resistance Army (LRA).

The LRA was forced out northern Uganda and into a lawless patch of jungle straddling the borders of South Sudan, Democratic Republic of Congo and the Central African Republic around 2005. It had been forced out of northern Uganda, where they had fought President Yoweri Museveni’s government for years.

The LRA is notorious for its brutality and for kidnapping children for use as fighters and sex slaves.

New York-based Human Rights Watch (HRW) said in a statement it had interviewed more than a dozen women and girls who accused soldiers of using food to manipulate them into abusive sexual acts. In some cases, the offending soldiers threatened their victims with reprisals if they reported the abuse, it said.

“Ugandan soldiers ... have sexually exploited or abused at least 13 women and girls since 2015, including at least one rape. Two of the women were girls when the exploitation or abuse took place,” HRW said.

Some of those interviewed told HRW they had become pregnant, and that the soldiers in all the cases had returned to their country and not offered any support.

Richard Karemire, Uganda’s military spokesman, said Uganda was investigating the sexual abuse allegations. Similar allegations were made by the U.N. High Commissioner for Human Rights, Zeid Ra’ad Al Hussein, in July last year.

“We have a comprehensive code of conduct and laws, so anyone going against that faces the music,” Karemire said. At least one soldier had already been arrested and prosecuted for attempted rape while deployed in Central African Republic, he said.

HRW said all the sexual abuse it documented took place around Obo, a town in the country’s south-east where the Ugandan military was based.

Last month, Ugandan authorities said they were starting to withdraw their forces from Central African Republic after significantly degrading Kony’s force. Kony, who has been indicted by the International Criminal Court for war crimes and crimes against humanity, remains at large.

“As counter-LRA operations wind down, Uganda’s military should not ignore allegations of sexual exploitation and rape by its soldiers,” HRW said.

The group asked both Uganda and the AU to “conduct proper investigations, punish those responsible”. Investigating and accounting for the alleged sexual offences in Central African Republic should be a condition for any future military aid to Uganda from the United States, the group said.